joshburgess

// in response to https://twitter.com/arntzenius/status/1022076441603829760

//  types  A,B ∷= base | A → B
//  terms  M ∷= E | λx.M
//  exprs  E ∷= x | E M | (M : A)
type Type = "Base" | {lhs: Type, tag: "->", rhs: Type};
type Var = string;
type Term = Expr | {tag: "Lam", varname: Var, body: Term};
type Expr = Var | {tag: "App", fn: Expr, arg: Term} | {term: Term, tag: ":", tp: Type};

joshburgess

const Day = ({ get, left, right }) => {
  const map = f => Day ({
    get: f (extract()),

    left, right
  })

  const extend = f =>
    Day ({
      get: (left, right) => f (Day ({ get, left, right })),

joshburgess

import R from "ramda";

module.exports = R.mapObjIndexed(R.invoker, {
    toJS: 0,
    toObject: 0,
    toArray: 0,
    keys: 0,
    reverse: 0,

    entrySeq: 0,

joshburgess

This is a port of the RemoteData type from Kris Jenkins article „How Elm Slays a UI Antipattern“ to TypeScript with TsMonad. There have been ports to Flow and JavaScript as well.

joshburgess

Technical overview

A basic Option type

// Option.ts

// definition
export class None {
  readonly tag: 'None' = 'None'

joshburgess

tsc && node main.js

joshburgess

// Types:
type Just<T> = { Just: T }
type Nothing = {}
type Maybe<T> = Just<T> | Nothing

type Left<L> = { Left: L }
type Right<R> = { Right: R }
type Either<L, R> = Left<L> | Right<R>

// For convenience:

joshburgess

/* 
  Slaying a UI Anti Pattern in ReasonML
  Based on Kris Jenkins original writing.
  http://blog.jenkster.com/2016/06/how-elm-slays-a-ui-antipattern.html
*/
type remoteData 'e 'a =
  | NotAsked
  | Loading
  | Failure 'e
  | Success 'a;

joshburgess

type Init<T extends any[], TTail extends any[] = TailArray<T>> = CastArray<{
  [K in keyof TTail]: T[keyof T & K];
}>

type PotentialArgs<T extends any[], TResult extends any[] = T> = {
  "continue": PotentialArgs<Init<T>, TResult | Init<T>>;
  "end": TResult;
}[T extends [] ? "end" : "continue"]

type Args<T extends Function> =

joshburgess

import { Monad, Monad1 } from 'fp-ts/lib/Monad'
import { HKT, URIS, Type } from 'fp-ts/lib/HKT'
import { liftA2 } from 'fp-ts/lib/Apply'
import { flatten } from 'fp-ts/lib/Chain'
import { Newtype, iso } from 'newtype-ts'

// Adapted from https://tech.iheart.com/why-fp-its-the-composition-f585d17b01d3

//
// newtypes